1. Field of the Invention
The invention relates to a hearing assistance system comprising a hearing device which comprises means for stimulating the user's hearing and which is to be worn at one of the user's ears and a remote device spaced apart from the hearing device, wherein a wireless link is established between the hearing device and the remote device in order to transmit signals from the remote device to the hearing device. The invention also relates to a method of operating such a hearing assistance system.
2. Description of Related Art
Examples of such hearing assistance systems are binaural hearing aids (in this case the remote device is a hearing instrument which is worn at the other one of the user's ears, with both hearing instruments being hearing aids comprising a microphone and an output transducer); in this case the link may serve as a bi-directional data link for exchanging audio signals, control data, and/or commands between the hearing aids.
Other examples of such a hearing assistance systems are CROS or BiCROS systems (in this case the remote device is a wireless microphone worn at the other one of the user's ears). In a CROS (also spelled CROSS) system the hearing instrument does not comprise a microphone, while in a BiCROS (also spelled BiCROSS) system the hearing instrument comprises a microphone, depending on whether the ear at which the hearing instrument is worn needs hearing assistance or not. In both cases the ear at which the wireless microphone is worn is essentially inaidable by a hearing instrument.
According to further examples of such hearing assistance systems the remote device is a remote control for the hearing instrument (in this case the link is for transmitting control data and/or commands from the remote control to the hearing instrument), an external microphone worn by another person (for example a teacher) or an external microphone worn by the user at a place other than the ears, or a device for wireless transmission of audio signal from a external audio signal source, such as a telephone, a television, an external microphone, a hi-fi-system, etc.
Generally, the receiver unit for the wireless link could be integrated within the hearing instrument/hearing aid, or the receiver unit could be a separate device which is mechanically and electrically connected to the hearing instrument/hearing aid, usually via an “audio shoe” in order to provide the audio signals received over the wireless link to an audio input of the hearing aid.
In such known systems the wireless link from the remote device to the receiver unit included in or connected to the hearing instrument may be heavily disturbed if a source of interfering radio frequency signals comes close to the hearing instrument. A typical example for such interfering radio frequency source is a mobile phone. Typically, a mobile phone transmits TDMA (time division multiple access) signals, for example according to the GSM (global system for mobile communications) standard. In this case transmission from the mobile phone occurs periodically, with only ⅛ of the time being used for transmission. A similar periodic transmission scheme is found in cordless telephone systems using the DECT standard; also in this case only a relatively small fraction of each period is used for transmission. This applies similarly also to devices using the Bluetooth standard.
If such interfering radio frequency source is brought very close to the hearing instrument worn had the user's ear, the link between the remote device and the hearing instrument may brake down, what is very inconvenient for the user. Such radio frequency sources may be considered as “burst interferes”.
Examples of wireless links for binaural hearing aid systems are found in U.S. Pat. No. 6,549,633 B1 and US 2004/0037442 A1.
According to US 2005/0117764 A1 the use of a DECT or GSM phone at one of the two sides of a hearing aid set is detected by analyzing the level difference between the left ear and right ear hearing coil in order switch the respective hearing aid to a phone mode.
According to U.S. Pat. No. 6,587,568 B1 and EP 1 501 200 A2 a hearing aid is capable of recognizing periodic RF (radio frequency) interference signals, for example from mobile phones, with the gain of the hearing aid being synchronized to the periodicity of the RF interference signals, so that the gain of the hearing aid is reduced or even set to zero during the presence of an interfering RF burst. According to US 2003/076974 A1 a hearing aid is capable of detecting the presents of characteristic RF interference signals in order to not only switch the gain of the hearing aid accordingly but also to switch other parameters, such as the filter band width, of the hearing aid accordingly. Thereby specific auditory scenes can be recognized, in particular the use of a telephone in order to adapt the operation mode of the hearing aid accordingly.
It is an object of the invention to provide for a hearing assistance system comprising a hearing device and a remote device, with a wireless link being established between the hearing device and the remote device for transmitting signals from the remote device to the hearing device, wherein the system should provide for a reliable wireless link even in the presence of a source of radio frequency signals interfering with the wireless link, which have a transmission power changing according to a predictable scheme. It is a further object to provide for a corresponding method for operating such a system.